RFB (the protocol used for VNC) implements at its base level rectangle-based updates which can be used to send over just rectangle-bound differences between frames. It's just that some shoddy server implementations send over the entire screen at once without damagerect tracking.

There's also plenty of extensions, some proprietary some not, which allow for more advanced compression/optimization: https://en.wikipedia.org/wiki/RFB_protocol#Encoding_types